A ceramic plate-like sintered body having a metal layer buried therein to work as a heater or an electrode, has been used as a plate for placing a semiconductor wafer such as silicon wafer thereon in an apparatus for producing a semiconductor by forming a film on the semiconductor wafer or etching the semiconductor wafer. For example, the one burying a metal layer therein as a heater is used as a plate heater, and the one burying an electrode therein is used as an electrostatic chuck. The electrostatic chuck further often has a metal layer buried therein to work as an electrode and as a heater.
As a ceramic material for use in the above applications in recent years, there has been used an aluminum nitride sintered body having a good thermal conductivity.
Due to an increased degree of integration as a result of technical innovation in recent years, further, it has been urged to further increase the precision. Besides, semiconductor wafers to be treated are becoming large in size. In a treatment for forming a film on the surface, for instance, it has been urged to form a uniform and thin film on the surface of the semiconductor wafer having a large area maintaining good precision. In the etching treatment, further, it has been urged to uniformly etch a variety of thin films having large areas formed on the semiconductor wafer.
In a plate-like sintered body of aluminum nitride used as the plate heater or the electrostatic chuck under the above circumstances, it is essential that the metal layer that is buried exists maintaining a uniform thickness from the semiconductor wafer placed on the sintered body.
To produce the plate-like sintered body of aluminum nitride burying the metal layer therein, there can be contrived a method of preparing a green sheet of aluminum nitride burying the metal layer therein, and firing the green sheet. According to this method, however, there remains a problem in that the metal layer is broken or deformed due to a change in the size during the sintering. Generally, therefore, a sintered body in the form of a plate or a sheet is prepared, and two sintered bodies are joined together via a metal layer. That is, the plate-like sintered body of aluminum nitride obtained by this method is in the form of a joined body in which two pieces of aluminum nitride sintered plates are joined together with a metal layer sandwiched therebetween effectively avoiding the above-mentioned problem caused by the dimensional change during the sintering.
When the aluminum nitride joined body is to be produced by the junction method, there is used an adhesive for joining the two pieces of sintered body plates. With the plate adhesive used so far, however, the adhering temperature is so high that the sintered body plates are deformed due to the heat at the time of junction arousing a problem of warping of the metal layer.
Therefore, a method has been proposed to improve the warping by using an adhesive which adheres at a decreased temperature (see Japanese Unexamined Patent Publication (Kokai) No. 2000-252045).
The above method improves the warping of the metal layer in the joined body to some extent still leaving, however, room for improvement. Besides, though the junction strength is maintained to a sufficient degree between the aluminum nitride layer and the metal layer, a problem still remains in that the junction strength decreases with the passage of time due to thermal hysteresis in the portions where the aluminum nitride sintered plates are directly faced to each other.